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\frac{\sqrt{18} * \sqrt[3]{54}}{\sqrt[3]{16}*\sqrt{72}}=\sqrt[3]{\frac{54}{16}}*\sqrt{\frac{18}{72}}=\sqrt[3]{\frac{27}{8}}*\sqrt{\frac{1}{4}}=
\sqrt[3]{(\frac{3}{2})^3}*\sqrt{(\frac{1}{2})^2}=\frac{3}{2}*\frac{1}{2}=\frac{3}{4}
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\frac{\sqrt6(\sqrt8-\sqrt{27})}{9\sqrt2 - 4\sqrt3}=\frac{\sqrt6(2\sqrt2-3\sqrt3)}{9\sqrt2-4\sqrt3}=\frac{2\sqrt{12}-3\sqrt{18}}{9\sqrt2-4\sqrt3}=
\frac{2*2\sqrt3-3*3\sqrt2}{9\sqrt2-4\sqrt3}=\frac{4\sqrt3-9\sqrt2}{9\sqrt2-4\sqrt3}=\frac{-(9\sqrt2-4\sqrt3)}{9\sqrt2-4\sqrt3}=-1